Convert a decoded Base64 byte string to a vector of bools - c++

Question

I have a base64 string containing bits, I have alredy decoded it with the code in here. But I'm unable to transform the resultant string in bits I could work with. Is there a way to convert the bytes contained in the code to a vector of bools containing the bits of the string?
I have tried converting the char with this code but it failed to conver to a proper char
void DecodedStringToBit(std::string const& decodedString, std::vector<bool> &bits) {
int it = 0;
for (int i = 0; i < decodedString.size(); ++i) {
unsigned char c = decodedString[i];
for (unsigned char j = 128; j > 0; j <<= 1) {
if (c&j) bits[++it] = true;
else bits[++it] = false;
}
}
}

Answer 1

Your inner for loop is botched: it's shifting j the wrong way. And honestly, if you want to work with 8-bit values, you should use the proper <stdint.h> types instead of unsigned char:
for (uint8_t j = 128; j; j >>= 1)
bits.push_back(c & j);
Also, remember to call bits.reserve(decodedString.size() * 8); so your program doesn't waste a bunch of time on resizing.
I'm assuming the bit order is MSB first. If you want LSB first, the loop becomes:
for (uint8_t j = 1; j; j <<= 1)

Answer 2

In OP's code, it is not clear if the vector bits is of sufficient size, for example, if it is resized by the caller (It should not be!). If not, then the vector does not have space allocated, and hence bits[++it] may not work; the appropriate thing might be to push_back. (Moreover, I think the code might need the post-increment of it, i.e. bits[it++] to start from bits[0].)
Furthermore, in OP's code, the purpose of unsigned char j = 128 and j <<= 1 is not clear. Wouldn't j be all zeros after the first iteration? If so, the inner loop would always run for only one iteration.
I would try something like this (not compiled):
void DecodedStringToBit(std::string const& decodedString,
std::vector<bool>& bits) {
for (auto charIndex = 0; charIndex != decodedString.size(); ++charIndex) {
const unsigned char c = decodedString[charIndex];
for (int bitIndex = 0; bitIndex != CHAR_BIT; ++bitIndex) {
// CHAR_BIT = bits in a char = 8
const bool bit = c & (1 << bitIndex); // bitwise-AND with mask
bits.push_back(bit);
}
}
}